KMP

#include<cstdio>
#include<cstring>
#include<iostream>
#include<string>
#include<memory.h>
using namespace std;

int count = 0;
string s,l;

void get_next(string src, int m, int *next)
{
    int i = 0,j = -1;
    next[0] = j;
    while (i < m) {
        while (j != -1 && src[j] != src[i])
            j = next[j];
        i++,j++;
        next[i] = j;
    }
}

void kmp(string s,int m, string l, int n)
{
    int next[10005];
    get_next(s,m,next);
    int i = 0,j = 0;
    while (i < n) {
        while (j != -1 && s[j] != l[i])
            j = next[j];
        i++,j++;
        if (j == m){
            count++;
            j = next[j];
        }
    }
}
int main()
{
    int t;
    cin >> t;
    while (t--) {
        count = 0;
        cin >> s >> l;
        kmp(s,s.length(),l,l.length());
        cout << count << endl;
    }
    return 0;
}

介绍有很多，觉得真正写得好,容易懂的博客:

http://blog.csdn.net/guo_love_peng/article/details/6618170